This invention relates to amine modified acidic resin catalysts and their use in the reaction of hydroxyaromatic compounds with aldehydes and ketones in the presence of a thiol promoter to afford bisphenols, such as bisphenol A (BPA).
Bisphenols, as exemplified by BPA, are widely employed in the manufacture of polymeric materials and are typically prepared by condensation of a hydroxyaromatic compound with an aldehyde or ketone in the presence of an acidic catalyst. Bisphenol A is the principal monomer used in the manufacture of bisphenol A polycarbonate, a commercial engineering thermoplastic material. The manufacture of bisphenol A from acetone and phenol is practiced globally on a large scale with hundreds of millions of pounds of BPA produced annually. Typically, phenol is reacted with acetone in the presence of an acidic catalyst and a thiol promoter. The thiol promoter acts to improve the rate and selectivity of BPA formation in the acid catalyzed condensation of phenol with acetone. Many different combinations of acidic catalysts and thiol promoters have been investigated and some thiol promoters such as 3-mercaptopropionic acid have been employed in the commercial scale production of BPA. Notwithstanding earlier research efforts and their attendant impressive process improvements in the manufacture of bisphenols, such as bisphenol A, there is a continuing need to improve further both the rate and selectivity of bisphenol formation in the acid catalyzed condensation of hydroxyaromatic compounds with aldehydes or ketones.
In one aspect the present invention relates to a method for making a bisphenol, said method comprising contacting a mixture comprising a hydroxyaromatic compound and a ketone or an aldehyde with an amine modified acidic resin catalyst at a temperature in a range between about 25xc2x0 C. and about 95xc2x0 C. in the presence of a thiol promoter. In a further aspect, the present invention relates to amine modified acidic resin catalysts.
The present invention may be understood more readily by reference to the following detailed description of preferred embodiments of the invention and the examples included herein. In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings.
The term xe2x80x9camine modified acidic resin catalystxe2x80x9d as used herein refers to an acidic resin, a portion of the acidic functional groups of which have been neutralized by treatment with an amine. For example a sulfonated polystyrene resin in which about 5 to 50 percent of the SO3H groups have been converted to the corresponding pyridium salts upon treatment of the resin with the corresponding amount of the amine, pyridine, constitutes an amine modified acidic resin catalyst. The amine employed is distinct from any thiol promoter which itself comprises an amine group. Where the thiol promoter contains an amine group, for example as in cysteamine, the amine modified acidic resin catalyst is understood to comprise at least one other amine which is not a thiol promoter.
xe2x80x9cBPAxe2x80x9d is herein defined as bisphenol A and is also known as 2,2-bis(4-hydroxyphenyl)propane, 4,4xe2x80x2-isopropylidenediphenol and p,p-BPA.
xe2x80x9co,p-BPAxe2x80x9d is herein defined as o,p-bisphenol A and is also known as 2-(2-hydroxyphenyl)-2-(4-hydroxyphenyl)propane and 2,4xe2x80x2-isopropylidenediphenol.
As used herein the term xe2x80x9caromatic radicalxe2x80x9d refers to a radical having a valency of at least one and comprising at least one aromatic group. Examples of aromatic radicals include phenyl, pyridyl, furanyl, thienyl, imidazolyl, naphthyl, phenylene and biphenyl groups. The term includes groups containing both aromatic and aliphatic components, for example a benzyl group. Further, a C3-C40 aromatic radical is an aromatic radical comprising between 3 and 40 carbon atoms. The 2-imidazolyl group (i) illustrates a C3 aromatic radical. 
As used herein the term xe2x80x9caliphatic radicalxe2x80x9d refers to a radical having a valency of at least one and comprising a linear or branched array of atoms which is not cyclic. The array may include heteroatoms such as nitrogen, sulfur and oxygen or may be composed exclusively of carbon and hydrogen. Examples of aliphatic radicals include methyl, methylene, ethyl, ethylene, hexyl, and hexamethylene groups.
As used herein the term xe2x80x9ccycloaliphatic radicalxe2x80x9d refers to a radical having a valency of at least one and comprising an array of atoms which is cyclic but which is not aromatic. The array may include heteroatoms such as nitrogen, sulfur and oxygen or may be composed exclusively of carbon and hydrogen. Examples of cycloaliphatic radicals include cyclopropyl, cyclopentyl cyclohexyl and tetrahydrofuranyl groups.
As used herein the term xe2x80x9ccarbamyl groupxe2x80x9d refers to a functional group comprising the array of atoms OCONH. For example a carbamyl group is present the product of reaction of an alcohol with an isocyante as illustrated by the compound 1-naphthyl methylcarbamate, CAS No. 63-25-2.
As used herein the term xe2x80x9cBoc groupxe2x80x9d refers to a an amine protecting group comprising the tertiary-butoxycarbonyl moiety. The combination of a nitrogen atom bearing both a hydrogen atom and the Boc group is an example of a carbamyl group.
The term xe2x80x9cthiol promoterxe2x80x9d as used herein refers to a molecule incorporating a thiol (SH) group. The thiol promoter acts to improve the rate and selectivity of bisphenol formation when a hydroxyaromatic compound is condensed with an aldehyde or ketone in the presence of an acidic catalyst relative to the same reaction carried out in the absence of the thiol promoter.
The term xe2x80x9csilylmethanethiolxe2x80x9d refers to a thiol compound in which a silicone atom and sulfur atom are each attached to the same carbon atom.
The instant invention provides a method of preparing a bisphenol, such as bisphenol A, by acid catalyzed condensation of a hydroxyaromatic compound, such as phenol, with an aldehyde, such as butanal, or a ketone, such as acetone, in the presence of a thiol promoter and an amine modified acidic resin catalyst.
The instant invention further provides amine modified acidic resin catalysts, which when used in the preparation of bisphenols, such as bisphenol A, provide selectivity advantages over known acidic resin catalyst systems. Amine modified acidic resin catalysts are prepared upon treatment of a polymeric material comprising acidic functional groups, such as sulfonic acid groups, with an amine in an amount such that between about 0.1 and about 50 percent of the acidic functional groups are neutralized. The amine modified acidic resins of the present invention are more selective catalysts, as measured by the greater selectivity for p,p-BPA formation observed when phenol and acetone are reacted in the presence of said amine modified acidic resin and a thiol promoter, relative to known acidic resin catalysts such as sulfonated polystyrene in combination with a thiol promoter.
Typically, the acidic resin catalyst which is converted to an amine modified acidic resin catalyst is a sulfonated polystyrene derivative comprising structural units I. Polymeric acidic resins comprising structure I are exemplified by 
Amberlyst(copyright) 131, Amberlyst(copyright) 15 and Amberlyst(copyright) 36, all of which are strongly acidic ion exchange resins available from the Rohm and Haas Company.
Other suitable polymeric acidic resin catalysts which may be converted into the amine modified acidic resin catalysts of the present invention include Nafion(copyright) perfluorinated acidic resins available from the Dupont Company.
Typically, the acidic resin catalyst possesses between about 0.1 and about 6, preferably between about 2 and about 5 milliequivalents of acidic functional group per gram of resin. Typically, the acidic functional group is a sulfonic acid group. In the practice of the present invention it has been found advantageous to treat the acidic resin catalyst with a sufficient amount of an amine to neutralize between about 0.1 and about 50 percent, preferably between about 5 and about 40 percent and most preferably between about 20 and about 35 percent of the acidic functional groups present in the acidic resin. Thus, treatment of one gram of a sulfonated polystyrene resin comprising structural units I possessing about 5 milliequivalents per gram resin of sulfonic acid groups (SO3H groups) with 1 milliequivalent of an amine, such as pyridine, affords an amine modified acidic resin catalyst in which 20 percent of the sulfonic acid groups have been converted to the corresponding pyridinium sulfonate salt, assuming complete reaction between the pyridine and the sulfonic acid groups of the resin. The amine modified acidic resin catalysts of the present invention are shown to be superior in terms of product selectivity relative to unmodified acidic resin catalysts. Product selectivity may be expressed as the weight percent of the p,p-bisphenol isomer in the product mixture relative to the weight percent o,p-bisphenol isomer. Additionally, product selectivity may be expressed as the weight percent of the desired p,p-bisphenol product relative to all other products formed.
Amines suitable for the preparation of amine modified acidic resin catalysts include aliphatic, cycloaliphatic and aromatic amines which are sufficiently basic to permit attachment of the amine to the resin, said attachment being based upon an ionic bond between the acidic group and the amine , such as is found in a pyridinium sulfonate.
Aliphatic amines are exemplified by triethylamine, trimethylamine, tributylamine and N,N-dimethylbutyamine. Cycloaliphatic amines are exemplified by piperidine, morpholine, 1,8-diazabicyclo[5.4.0]undec-7ene (DBU) and diazabicylco[2.2.2]octane (Dabco). Aromatic amines are illustrated by pyridine, imidazole, quinoline and piperazine. Generally, simple C1-C10 aliphatic, C4-C10 cycloaliphatic and C5-C9 aromatic amines are preferred.
Thiol promoters which may be employed include aliphatic, cylcoaliphatic and aromatic thiols which may be substituted by a basic group such as an amine or an acidic group such as a carboxylic acid. The thiol promoter may be used as a xe2x80x9cbulkxe2x80x9d promoter, that is a thiol promoter which is not adapted for attachment to the amine modified acidic resin, or an xe2x80x9cattachedxe2x80x9d promoter. Where the thiol promoter contains a basic functional group such as an amine said thiol promoter may be attached to amine modified acidic resin catalyst and is referred to as an xe2x80x9cattachedxe2x80x9d promoter. Functional groups present in the thiol promoter, other than amino groups, which facilitate the attachment of the thiol promoter to the amine modified acidic resin catalyst include amido, imido and carbamyl groups as are found in amides, imides and carbamates, respectively.
Bulk thiol promoters include cylcoaliphatic thiols such as cyclohexanethiol and cyclopentanethiol, aromatic thiols such as thiophenol and benzylthiol, and aliphatic thiols such as butanethiol, hexanethiol, octadecanethiol and 3-mercaptopropionic acid.
Attached thiol promoters include 2-mercaptomethylpyridine, cysteamine, and 4-aminobutanethiol immobilized in an amine modified acidic resin catalyst, for example a sulfonated polystyrene in which about 20 percent of the sulfonic acid groups have been neutralized with pyridine.
Among the aliphatic thiols suitable for use in the present invention silylmethanethiols having structure II have been found to be particularly effective thiol promoters. 
wherein R1 and R2 are each independently hydrogen, a C1-C40 aliphatic radical, a C3-C40 aromatic radical, a C3-C40 cycloaliphatic radical, or
R1 and R2 together form a C3-C40 cycloaliphatic radical or a C4-C40 aromatic radical;
R3-R5 are each independently a C1-C40 aliphatic radical, a C3-C40 aromatic radical, or a C3-C40 cycloaliphatic radical; or
any two of the groups R3-R5 together form a C5-C40 cycloaliphatic radical or C5-C40 aromatic radical; or
the groups R3-R5 together form a C9-C40 cycloaliphatic radical or C10-C40 aromatic radical.
Where any of the groups R1-R5 of structure II contains a basic functional group, such as an amino group, the silylmethanethiol promoter may be attached to the amine modified acidic resin catalyst. Functional groups present in the silylmethanethiol, other than amino groups, which facilitate the attachment of the promoter to the amine modified acidic resin catalyst include amido, imido and carbamyl groups as are found in amides, imides and carbamates, respectively.
Silylmethanethiols having structure II are known in the chemical 
literature and methods for their preparation have been described in, for example, J. Org. Chem. 53(5) 844 (1987); J. Org. Chem. 51(18) 3428 (1986); and Tetrahedron Letters 26 (11) 1425 (1985). In some instances silylmethanethiols having structure II are commercially available as in the case of trimethylsilylmethanethiol which is available from TCI Chemical Company, Portland, Oreg. Other members of this class may be prepared by reaction of a chloromethylsilane having structure III with a sulfur nucleophile such as sodium sulfide, sodium thioacetate or thiourea. Where sodium sulfide is employed the silylmethanthiol II is obtained directly. Where the thioacetate is employed as a nucleophile, acetate derivative IV is obtained. The acetate derivative IV is readily converted to the corresponding thiol II upon solvolysis, for example upon heating acetate derivative IV with methanol in the presence of a basic catalyst such as triethylamine.
Chloromethylsilicon compounds corresponding to structure III may be prepared by a variety of methods, among them the hydrosilylation reaction of olefins having structure V with a chloromethylsilane VI incorporating a silicone hydride function. Thus, olefin V in which radical R6 corresponds to a two carbon lower homolog of radical R5 may be reacted with chloromethylsilane VI in the presence of a noble metal catalyst to afford chloromethylsilicon derivative III.
A variety of reaction conditions may be employed for the conversion 
of chloromethylsilanes III into silylmethanethiols II and silylmethanethiol acetate derivatives IV. Typically, the chloromethylsilane III is combined in a polar solvent such as methanol or dimethylformamide with a slight excess of sodium sulfide or sodium thioacetate and the mixture us stirred at a temperature between about 0xc2x0 C. and about 100xc2x0 C. until the starting chloromethylsilane III has been consumed as judged by gas chromatography, thin layer chromatography or like analytical technique. Thereupon, the reaction mixture may be distributed between water and a solvent such as methylene chloride, toluene or ethyl acetate. The organic layer is then washed with water to complete the removal of inorganic salts and then dried over a suitable drying agent such as magnesium sulfate. Filtration and solvent evaporation affords the crude product which may be employed as a thiol promoter for BPA production in its crude state, or purified, for example by column chromatography or recrystallization, prior to such use.
Examples of silylmethanethiols which may be used as promoters for bisphenol production include, but are not limited to, trimethylsilylmethanethiol, triethylsilylmethanethiol, tripropylsilylmethanethiol, tributylsilylmethanethiol, 1-trimethylsilyl-1-ethylmethanethiol and 1-trimethylsilyl-1-benzylmethanethiol.
Where the silylmethanethiol promoter is to be used as a bulk promoter, the preferred silylmethanethiol promoter is trimethylsilylmethanethiol owing to its availability, ease of preparation and recovery or removal from the reaction product.
In some instances it may be advantageous to employ a silylmethanethiol derivative such as trimethylsilylmethanethiol acetate in the process of the present invention. Under such circumstances it is believed that the silylmethanethiol acetate is converted to the active silylmethanethiol promoter under the reaction conditions. Silylmethanethiol acetates and other silylmethanethiol derivatives which afford a silylmethanethiol under the reaction conditions are advantageously employed at about the same levels as the silylmethanethiol itself.
In some instances the silylmethanethiol promoter may function as an attached promoter, as is the case of those silylmethanethiols which incorporate an amine function which may be used to form an attachment to amine modified acidic resin catalyst. The attachment of the silylmethanethiol to the amine modified acidic resin catalyst may be based upon a strong hydrogen bonding interaction or a covalent bond. Examples of silylmethanethiols which may be used as attached promoters for bisphenol production include 3-aminopropyldimethylsilylmethanethiol, 3-N-methylaminopropyldimethylsilylmethanethiol, 3-N,N-dimethylaminopropyldimethylsilylmethanethiol, 3-(1-piperadinyl)propyldimethylsilylmethanethiol and 2-(4-pyridyl)ethyldimethylsilylmethanethiol.
In addition to silylmethanethiols which incorporate a free amino function, derivatives of such materials incorporating acylated thiol groups and protected amine groups may also be employed. Thus, the N-Boc-3-aminopropyldimethylsilylmethanethiol acetate derivative VII is found to function as an effective attached promoter for bisphenol production. Thioacetate VII is believed to be converted to 3-aminopropyldimethyl-silylmethanethiol VIII under the conditions used to prepare bisphenols. 
As noted, the instant invention provides a method of preparing a bisphenol, such as bisphenol A, wherein an amine modified acidic resin catalyst is employed together with a thiol promoter to effect the condensation of a hydroxyaromatic compound with an aldehyde or a ketone. Examples of hydroxyaromatic compounds include phenol, o-cresol, m-cresol, 2-t-butylphenol, 2-propylphenol and 1-naphthol. Examples of aldehydes include formaldehyde, acetaldehyde, propionaldehyde and butanal. Examples of ketones include acetone, cyclohexanone; 3,3,5-trimethylcyclohexanone, 2-butanone and fluorenone.
A wide variety of bisphenols; such as 2,2-bis(4-hydroxyphenyl)propane; 2,2-bis(4-hydroxy-3-methylphenyl)propane; 1,1-bis(4-hydroxyphenyl)cyclohexane; 1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, may be prepared by the method of the present invention. The present invention is best exemplified by its use in the preparation of bisphenol A via condensation reaction of the hydroxyaromatic compound, phenol, and the ketone, acetone. A mixture comprising phenol and acetone may be contacted with an amine modified acidic resin catalyst and thiol promoter at a temperature between about 20xc2x0 C. and about 100xc2x0 C., preferably between about 40xc2x0 C. and about 90xc2x0 C. and still more preferably between about 50xc2x0 C. and about 80xc2x0 C.
The method of the present invention may be employed in both batch and continuous processes. When the method of the present invention is employed as a continuous process, the amine modified acidic resin catalyst may be configured in a fixed bed or stirred tank reactor such that the reactants, phenol, acetone and the thiol promoter are presented to the catalyst and removed from the catalyst in a continuous fashion. Alternatively, the amine modified acidic resin catalyst may be pretreated with the thiol promoter containing a functional group such as an amine or a carbamate capable of attachment to the amine modified acidic resin catalyst. The use of an attached thiol promoter obviates the need to include thiol promoter in the feed stream comprising phenol and acetone. Where a thiol promoter containing a basic functional group is employed, it may be attached to the amine modified acidic resin itself or it may be included in the during the preparation of the amine modified acidic resin from an unmodified acidic resin.
When the method of the present invention is employed as a continuous process, the reactants are combined to give a feed mixture said mixture being introduced at a weight hourly space velocity of from about 0.1 to about 6, preferably from about 1 to about 4, and even more preferably from about 2 to about 3.5 pounds of the feed mixture per pound catalyst per hour. The feed mixture comprises from about 0.1 to about 10 weight percent acetone and about 70 to about 99 weight percent phenol, preferably about 3 to about 8 weight percent acetone and about 85 to about 96 weight percent phenol, and still more preferably about 3 to about 6 weight percent acetone and about 90 to about 96 weight percent phenol. When employed as a bulk promoter, the thiol promoter may be present in an amount in a range between about 5 and about 100, preferably about 10 and about 75, and even more preferably about 20 and about 40 millimoles per liter (mmol/L) of feed. When employed as an attached promoter the thiol is present in an amount in a range between about 0.1 and about 3, preferably about 0.5 and about 2 milliequivalents per gram amine modified acidic resin catalyst.